From e91fbebe3d5560373a3e069a66dbe2eed5850a57 Mon Sep 17 00:00:00 2001
From: "Howard M. Harte" <hharte@magicandroidapps.com>
Date: Sat, 5 Nov 2022 19:55:40 -0700
Subject: [PATCH] AltairZ80: i86: Don't clear segment override on REPE/REPNE

MASM generates REP CS:MOVSW as:

REP
CS:
MOVSW

The Seattle Computer Products 8086 assembler allows the segment override
as a discrete opcode.  This means that:

CS:
REP
MOVSW

is also possible, and in fact used in the SCP Monitor v1.6.

The i86 emulator was clearing the override flags when REPE/REPNE,
is encountered, which causes the segment override to be lost.
Verifying the behavior of a real 80286 processor in an IBM PC/AT
(5170) using MS-DOS 6.22 DEBUG shows that both instruction sequences
yield the desired segment override.
---
 AltairZ80/i86_ops.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/AltairZ80/i86_ops.c b/AltairZ80/i86_ops.c
index de2b8fab..f652b237 100644
--- a/AltairZ80/i86_ops.c
+++ b/AltairZ80/i86_ops.c
@@ -4321,14 +4321,12 @@ static void i86op_lock(PC_ENV *m)
 static void i86op_repne(PC_ENV *m)
 {
    m->sysmode |= SYSMODE_PREFIX_REPNE;
-   DECODE_CLEAR_SEGOVR(m);
 }
 
 /*opcode=0xf3*/
 static void i86op_repe(PC_ENV *m)
 {
    m->sysmode |= SYSMODE_PREFIX_REPE;
-   DECODE_CLEAR_SEGOVR(m);
 }
 
 /*opcode=0xf4*/